Predicting outcome in patients with rhabdomyosarcoma: role of [(18)f]fluorodeoxyglucose positron emission tomography

To evaluate whether [(18)F]fluorodeoxyglucose positron emission tomography (FDG-PET) response of the primary tumor after induction chemotherapy predicts outcomes in rhabdomyosarcoma (RMS).

After excluding those with initial tumor resection, 107 patients who underwent FDG-PET after induction chemotherapy at Memorial Sloan Kettering Cancer Center from 2002 to 2013 were reviewed. Local control (LC), progression-free survival (PFS), and overall survival (OS) were calculated according to FDG-PET response and maximum standardized uptake value (SUV) at baseline (PET1/SUV1), after induction chemotherapy (PET2/SUV2), and after local therapy (PET3/SUV3). Receiver operator characteristic curves were used to determine the optimal cutoff for dichotomization of SUV1 and SUV2 values.

The SUV1 (<9.5 vs ≥9.5) was predictive of PFS (P=.02) and OS (P=.02), but not LC. After 12 weeks (median) of induction chemotherapy, 45 patients had negative PET2 scans and 62 had positive scans: 3-year PFS was 72% versus 44%, respectively (P=.01). The SUV2 (<1.5 vs ≥1.5) was similarly predictive of PFS (P=.005) and was associated with LC (P=.02) and OS (P=.03). A positive PET3 scan was predictive of worse PFS (P=.0009), LC (P=.05), and OS (P=.03).

[(18)F]fluorodeoxyglucose positron emission tomography is an early indicator of outcomes in patients with RMS. Future prospective trials may incorporate FDG-PET response data for risk-adapted therapy and early assessment of new treatment regimens.